Parenteral alimentation of sheep and swine will be used as the basis of a comparative model for studying nutrient requirements and metabolism under controlled input condition. The metabolic amino acid requirements and minimum energy intake for both species will be established as a baseline for comparative studies into questions which are important in the medical use of parenteral feeding. The source and amount of energy from glucose vs fat and the tolerance of both species to these nutrients, the influence of these compounds on insulin levels and the reaction of the animals to infused insulin will be studied. The utilization of, and tolerance for nitrogen sources other than essential L-amino acids, such as urea, non-essential amino acids, D- and DL- forms of amino acid will be investigated. The disappearance of N15 labelled amino acids from the serum and the appearance of the label in tissues and urine will be used to study amino acid metabolism in infused animals. These studies may serve as models for amino acids experiments in humans using this stable isotope.